1) Read quickly, but not too quickly.
I pause after each paragraph, make sure that I’ve understood the gist, and quickly decide on a couple of key words to circle. This ensures that I haven’t read so quickly that nothing was absorbed. Circling key words gives me something concrete to do to nail down the content, rather than just thinking ‘Okay, yeah, I got that. Moving on…’

2) Stop after the passage, too.
This is based on Kaplan’s Topic/Scope/Purpose strategy, but simplified. I try to summarize the point (purpose) of the passage in one sentence/phrase in my head. This step is crucial to answering those ‘What is the central theme’ questions. Again, if you can’t come up with something for this step, then you haven’t done a good job of reading.

3) Whenever possible, try to predict answers before looking at the options. (Obviously doesn’t work for necessarily process-of-elimination questions.)
Sample question: "In paragraph 2, the author strengthens the argument by…". Don’t look at the options. Look at paragraph 2 (if you don’t remember what it was about), especially at the key words that you identified. Formulate a quick answer in your head. Then look at the given options to choose the one that most closely matches. This is a combination of "going with your gut instinct" tempered with "not getting distracted by wrong answers."

4) Keep it simple!
Unless I can’t avoid it, I ignore all subtleties/nuance in the original passage. Think structurally. Think in black & white. Identify contrasts, comparisons, support; I often paraphrase paragraphs as "this vs. that", or "x = y" or "support for previous paragraph" or "opposition to previous paragraph".

Remember– in VR, the wrong answer options are especially tricky. They’re designed to look like right answers. Wrong answers are often relevant to the passage, but not to the particular question.

So make sure, first of all, that you have a good handle on the overall point of the passage, as well as the purpose of each paragraph within that passage. Then make sure that you understand the specific question. Then make sure, when you’re tempted by a specific answer, that you’re not just picking it because it superficially "sounds good", but because it actually is the right answer to the right question.

Outside knowledge is definitely a big no-no on the Verbal Reasoning section, whether on natural science passages or any other type. There have been times when some of my students have known enough about a passage topic to be able to argue the point with the author; don’t do this. For the purpose of the MCAT, go with what the author says, even if you believe that s/he is full of, ahem, excrement. You are being tested on your ability to understand the author’s argument and apply it to new scenarios, NOT on the objective validity of the argument. So stay focused on the point the author is making, and don’t ever think about your own beliefs on the topic.

To answer questions that ask you to choose a reasonable conclusion or assumption for an argument, it’s important to understand what it means for a conclusion or assumption to be reasonable in the context of the MCAT.

An implied conclusion is necessarily supported by the evidence but is not explicitly stated. That is, given A, B, and C facts or assertions from the passage, conclusion X must be true. Look for something that HAS to be true given the evidence in the passage. (To check this, see what happens if you say your chosen answer is NOT true. Does it make the argument in the passage fall apart?)

An assumption is an implicit piece of evidence that has to be true in order to build an argument. It is part of the evidence but is not explicitly stated. As with the implied conclusions, you can figure out whether a statement is an assumption by attempting to falsify it. If you falsify an assumption, the entire argument that rests on it will fall apart.

Here’s an (obvious) example of these concepts. I just moved, and while unpacking I couldn’t find my box cutter. I told my mom "Only you and I packed boxes, and *I* didn’t pack the box cutter into a box." The (unstated) conclusion there is that my mom was the one who packed it into a box (useful place for a box cutter, eh?). The assumption, as you might have noticed, is that the box cutter WAS packed into a box, as opposed to riding in the glove compartment or something.

While I’m analyzing arguments, let’s talk about strengthening/weakening again. I could strengthen my argument by supporting either the facts or the assumption implicit in the argument. Examples of this: No one else who helped me move packed any boxes. It is discovered that the box cutter is not in the U-Haul truck. To weaken the argument, again, I can either contradict the facts or attack the assumption. For example: My dad packed two boxes. A grocery bag full of important stuff was packed and carried in the front seat of the car.

Basically when you come to one of these questions, the first thing you have to know is - what is the author’s argument? What assertions does s/he put forward, and what conclusions does s/he draw? Something that strengthens the argument will very often be something that supports the assertions - more data, or something that lets you know the author’s assumptions are correct. On the contrary, something that weakens the argument will contradict the author’s evidence or assumptions, or show that the conclusions don’t necessarily follow. So you have to be really clear on what argument the author is making. Then, you can frequently predict the type of answer that would strengthen or weaken the argument (though obviously you can’t predict the exact answer).

If you need help with how to identify the argument, see the post that QofQuimica and I have written about how to find the author’s viewpoint. Nutmeg also wrote a good post about distinguishing facts and opinions. I think the overall best question to ask yourself is: WHY did the author take the time to write this passage? What is it that they’re trying to convince the reader of? If you figure out why someone would bother to spend all that time writing something, you know what the overall point is, and the purpose of the argument.